Semiconductor devices are built in manufacturing environments known in the art as clean rooms, which are specifically designed for the filtering and elimination of particulate contaminants. Particle control is vital to the success of semiconductor manufacturing and directly affects device yield, as a single "killer" particle adhering to a device surface may ruin an entire microelectronic circuit. Such "killer" particles need not be large, but are generally of a size at least half the width of conductor wirings and other circuit features. As such, a 0.2 micron particle adhering to a circuit with 0.8 micron features may rarely cause a malfunction, while the same particle adhering to a circuit with 0.35 micron features is much more likely to "kill" the circuit.
Despite the clean manufacturing environment, cleanup steps must generally be performed throughout the semiconductor manufacturing operation to remove particles from the wafers, or slices, upon which the circuits are fabricated. Cleanup steps are particularly important before critical processes such as lithography and after inherently dirty processes such as chemical-mechanical polishing (CMP). For instance, CMP machines typically used for planarizing or smoothing a semiconductor wafer surface employ a polish slurry containing generally sub-micron sized abrasive particles of a material such as silica or alumina. Hundreds to thousands of these particles, along with particles removed from a wafer itself during polishing, typically may be found on a polished wafer surface. These particles must be removed in a cleanup step or they may drastically affect device yield.
Many methods of cleanup are common to semiconductor processing, including acid rinses, rinses with deionized (DI) water or surfactant solutions, and ultrasonic, brush, or mechanical buffing cleaning using such rinses and solutions, and combinations of these. For instance, U.S. Pat. No. 5,320,706, issued Jun. 14, 1994 to Blackwell, discloses a method for removing polish slurry particles from a semiconductor wafer by polishing the wafer with a polishing pad while a mixture of DI water and a surfactant is applied to the wafer and the pad. This method is apparently capable of reducing the number of residual particles on a 5" wafer to about 100 of 0.5 micron size and larger. Unfortunately, particle count varies roughly exponentially with particle size; that is, if 100 0.5 micron particles remain on a wafer after cleaning, it is likely that a thousand or more 0.2 micron particles remain also, each of which is capable of killing a 0.35 micron feature size circuit. Much more effective cleaning methods are required as circuit feature sizes continue to shrink, if acceptable yields are to be maintained.